Conventionally, a plurality of printed circuit boards are arranged in parallel on a substrate called a backboard, and an electronic device accommodating such a structure in a card basket is used.
The backboard is provided with a plurality of connectors to connect to the printed circuit boards, and is electrically connected to the circuit patterns (power supply, signal, ground, and the like) of the printed circuit boards via the connector pins of the respective connectors.
The signal GNDs (SG: signal ground) of the plurality of printed circuit boards are electrically connected via the connector pins of the respective connectors of the backboard. Thus, a potential difference occurs among the signal GNDs of the printed circuit boards due to the impedance of the connector pins, making unstable the circuit operations of the printed circuit boards.
Furthermore, in order to avoid electromagnetic noise (for example, lightning surge) occurring outside the electronic device from flowing to the signal GND of the printed circuit board, the signal GND of each printed circuit board is insulated from the card basket that serves as a frame GND (FG: frame ground). Therefore, if electromagnetic noise occurs in the signal GND of the printed circuit board, the electromagnetic noise cannot be released to the outside of the electronic device, making unstable the circuit operation of the printed circuit board.